1. Technical Field
The present invention relates to highly sensitive positive photoresist compositions which are mixtures of certain partially substituted polymeric materials and cationic photoinitiators. In particular, there are provided photoresist compositions with greatly improved sensitivity without deterioration of their processability. These compositions which may be conveniently developed with alkaline developers display increased sensitivity to ultraviolet (UV), electron beam (E-beam) and X-ray radiation, are thermally stable at temperatures up to about 165.degree. C., adhere readily to silicon dioxide and silicon nitride layers on a substrate, and may be treated with organometallic reagents (e.g., silylating agents) without the necessity of any post development baking. The films formed may be processed with very little image shrinkage on exposure and development and provide essentially crack-free resist layers. The partially substituted polymeric materials comprise recurrent structures having alkaline soluble groups pendent to the polymeric backbone, a portion of which groups have been substituted with (protected by) acid labile groups.
2. Background of the Invention
The fabrication of semiconductor devices requires the use of resist compositions which maintain imaged patterns during a processing. As the need to increase semiconductor circuit density has dictated a movement from very large scale integration (VLSI) devices to ultra-large scale integration (ULSI) devices, the demands for submicron photolithography with sensitivity to produce and maintain ultra-fine tolerances become more critical.
Chemically amplified resist systems having a polymer and sensitizer combination which generate an initial acid from the sensitizer and additional acid from the polymer provide increased sensitivity to UV, e-beam and x-ray radiation.
In Ito et al., U.S. Pat. No. 4,491,628, resists sensitive to ultraviolet (UV), electron beam and X-ray radiation capable of forming either positive or negative tone patterns dependent upon the choice of developers were disclosed. Such resist compositions are formulated from a polymer having recurrent acid labile groups (such as tertbutyl esters and tertbutyl carbonates) which undergo efficient acidolysis to effect a change in polarity (solubility) and a photo-initiator which generates acid upon radiolysis. The polymer may be a copolymer which includes polymers having recurrent acid labile groups. When being used to form positive images the Ito materials have possibility drawbacks that are directly related to the completeness of removal of the acid labile group on the film composition. These factors relate to skin formation, shrinkage, cracking and poor adhesion which require delicate control to overcome.
In Ito et al., U.S. Pat. No. 4,552,833, there is provided a process for generating negative images wherein a film of a polymer having masked functionalities is coated onto a substrate, the film is imagewise exposed, the exposed film is treated with an organometallic reagent, and the treated film is developed with an oxygen plasma. That disclosure contemplates the dry development of polymers similar to those disclosed in U.S. Pat. No. 4,491,628. The dry development process avoids changes in film compositions that lead to processing complications
In Chiong et al., U.S. Pat. No. 4,613,398, still other processes are disclosed entailing the removal of acid labile protecting groups from pendent alkaline soluble groups on a resist polymer such as hydroxyl, amine, carboxyl, phenol, or imide NH which are capable of reacting with the organometallic reagent. Upon silylation and further processing negative images are obtained.
In U.S. Ser. No. 922,657, filed Oct. 24, 1986 now abandoned and assigned to the assignee of the present application, there are described certain highly sensitive resists that achieve high autodecomposition temperatures due to the presence of secondary carbonium ion forming acid labile substituent groups on polymers having pendent carbonate or carbonate-like groups.
Ito, J. Polymer Science Part A, 24, 2971-80 (1986) discloses effects of p-hydroxystvrene groups in the thermolysis of poly(p-t-butyloxycarbonyloxy styrene) and devises a method to make such substituted polymer via a copolymerization of butyloxycarbonyloxy styrene with formyloxy styrene followed by photo-fries decomposition to convert the formyloxystyrene units to hydroxystyrene units.